Leak detector for enclosed electrical apparatus

ABSTRACT

A detector for sensing the presence of a leak in a sealed, fluid-filled enclosure for electrical apparatus. The detector includes means for determining when the pressure within the enclosure is substantially equal to the pressure without the enclosure. When such a condition has existed for a preselected time period a warning device is actuated to indicate the existence of a leak in the enclosure.

United States Patent 1 1 1 1 3,731,295

Van Luyn 1 51 May 1, 1973 I541 LEAK DETECTOR FOR ENCLOSED 2,553,291 51951 Barr ..200/83 D ELECTRICAL PP RATU 3,365,710 1/1968 Duplessy..340/242 3,233,234 2 1966 St I h .340 38 L [75] inventor: Robert VanLuyn, Rome, Ga. I e mac l [73] Assignee: General Electric CompanyFOREIGN PATENTS APPLICATIONS [22] Filed: Mar. 17, 1971 709,436 8/1931France ..340/240 [211 App]. No.: 125,121 Primary Examiner.lohn W.Caldwell Assistant Examiner-Daniel Myer 52 us. c1. ..340/242 73/493174/11 R Frank Neuhause" '200/83 317/14 Oscar B. Waddell and Joseph B.Forman [51] Int. Cl. ..G08b 21/00 [58] Field of Search ..340/3s L, 240,242; [571 ABSTRACT 200/83 R, 83 Dino/54, 61, 33,6; 317/141 A detectorfor sensing the presence of a leak in a R, 14 G, 14 1-1, 14 J; 174/11 R;73/492, 49.3; sealed, fluid-filled enclosure for electrical apparatus.338/41 The detector includes means for determining when the pressurewithin the enclosure is substantially equal to [56] Rehrences cued thepressure without the enclosure. When such a con- UNITED STATES PATENTSdition has existed for a preselected time period a warning device isactuated to indicate the existence of 2,182,637 12/1939 Marbury..317/141 R a leak in the enclosure. 3,171,065 2/1965 Kingetal ..317/141R 3,356,922 12/1967 Johnston ..320/54 X 5 Claims, 1 Drawing Figure I I iI l l 1 l I l l A9 I 10 Y L I m 1 "272115 5 I 1 FRODUC/NG 5 MEANS iPatented May 1, 1973 MEA IVS WA RN/NG @S/GNA L PRODUCING nvvzmron:ROBERT VAN Luv/v TTOR/VEY LEAK DETECTOR FOR ENCLOSED ELECTRICALAPPARATUS BACKGROUND AND OBJECTS OF THE INVENTION This invention relatesto protective equipment for enclosed electric power apparatus, and moreparticularly it relates to leak detectors for sealed enclosurescontaining electrical apparatus immersed in a body of dielectric fluid.

In the art of power transmission and distribution it is a commonpractice to employ electrical apparatus enclosed in a sealed tankcontaining dielectric fluid, as for example fluid immersed powertransformers, reactors, switchgear or the like.

Fluid immersed electrical apparatus of the sealed tank type is commonlyfilled or partially filled with an insulating gas or liquid. In thisliquid filled apparatus a gas space is usually provided above the liquidsurface to serve as an expansion space for the liquid. This space isusually filled with a neutral gas such as nitrogen or air.

During the operational period when a liquid-filled transformer issupplying substantial load current, the liquid surrounding its coilswill be heated by the passage of current and will expand appreciably.Conversely, during a period of light loading the dielectric fluid willbe enabled to cool and thus contract. In most cases the high loadingperiod on a transformer occurs during the day and the low loading periodoccurs during the evening. In any event, when the'dielectric liquid isheated up as a result of a large imposed load, the pressure within thetransformer tank will increase above atmospheric pressure (suchincreased pressure will be hereinafter denoted as positive pressure).When the dielectric fluid cools down the pressure within the tank willdrop below atmospheric pressure (such decreased pressure willhereinafter be denoted as negative pressure).

If there is a leak in the transformer tank, the pressure within the tankwill be approximately equal to the pressure outside the tank although aslight pressure differential will exist. The magnitude of this pressuredifferential is a function of the magnitude of the transformer load andof the size of the leak in the tank (e.g., the smaller the tank leak,the greater the pressure differential for a given difference in loadmagnitude). Accordingly, if a leak exists, during the periods that thetransformer is supplying a large load, only a slight positive pressurewill build up in the tank. Nevertheless, even the slight positivepressure will result in the expulsion of some of the neutral gascontained in the tank. During periods that the transformer is supplyinga small load the pressure in the tank will be slightly negative and somecool, moist, outside air will be drawn into the tank. Over a long periodof time, e.g., several weeks or months, the recurring slight pressurechanges inside the tank will enable a sufficient amount of water vaporto enter the tank and to accumulate therein to impair the operationalcapability of the transformer by degrading the dielectric fluid and thesolid electrical insulation.

Merely detecting when the pressure within the trans- ,forrner tank isequal to the ambient pressure outside the tank, as a number of prior artleak detectors do, is not a reliable indication of the existence of atank leak since such a condition will naturally occur, even absent aleak, between periods of high and low transformer loading as thedielectric fluid is either heated or cooled.

Accordingly, it is a general object of my invention to providemeans forreliably detecting the presence of a leak in a sealed enclosure,dielectric-fluid-filled, electrical apparatus.

It is a further object of my invention to provide means for reliablydetecting the presence of a leak in a sealed ,enclosure,dielectric-fluid-fllled, electrical apparatus and for providing awarning signal indicative of such a condition.

SUMMARY OF THE INVENTION In carrying out my invention in one form, Iprovide a detector for determining the presence of a leak in sealedenclosure, dielectric-fluid-filled, electrical apparatus and forproviding a warning signal indicative of such a condition. My detectoroperates by monitoring the pressure within the apparatus enclosure. Ifthe pressure within the enclosure is substantially equal to the pressureoutside the enclosure for a predetermined period of time, a warningsignal is provided to indicate the existence of a leak in the apparatusenclosure.

The detector comprises movable means which responds to the pressureexisting within the enclosure. The movable means is coupled to adischargeable energy storage means and to an energy source. Means areprovided, coupled to the movable means, to enable the energy source tosupply energy to the energy storage means except when the pressurewithin the enclosure is substantially equal tothe pressure outside theenclosure. Signal warning means are provided coupled to the energystorage means. The signal warning means provides a warning indicationwhenever the energy storage means has discharged below a preselectedlevel.

BRIEF DESCRIPTION OF THE DRAWING My invention will be better understoodand its various objects and advantages will be more fully appreciatedfrom the following description taken in conjunction with theaccompanying drawing which is a schematic diagram of my leak detector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As can be seen in thedrawing a leak detector 1, in accordance with my invention, is showncoupled to the enclosure or tank 2 of a transformer. The transformertank is sealedand: houses the transformer coils (not shown), which areimmersed in a dielectric liquid (not shown), such as oil, to provide thenecessary electrical insulation therefor. The leak detector functions toprovide a warning signal upon the detection of 'theleak in the tank.

As was previouslyv noted the pressure within the sealed tank of a fluidfilled transformer will vary depending upon the magnitude of the loadbeing supplied. Absent a leak in the tank, during periods of highloading there will be a positive pressure within the tank,

I while during periods of low loading a negative pressure will exist.Accordingly, during the transition from a low :hereinafter referred to'as a substantial pressure balance?" also exists when there is a leak inthe transformer tank. It follows then, that the mere determination ofthe existence of a substantial pressure balance" is not a sufficientlyreliable indication of the presence of a tank leak since such a balancemay be merely transitional rather than leak representative.

My leak detector does more than merely detect the presence of asubstantial pressure balance and in so doing is capable of reliablydetermining the existence of a leak in the transformer tank. 1 havefound that if the pressure within the tank stays within the narrowpressure range between slightly positive pressure (e.g., plus mm ofmercury) and slightly negative pressure (e.g., minus 10 mm of mercury)for a relatively long period of time (e.g., 24 hours) this is indicativeof the existence of a leak in the transformer'tank. Therefore, Ihavedesigned detector 1 to be unresponsive to short duration substantialpressure balances (e.g., transitional pressure balances) but to respondto relatively long duration (e.g., 24 hours) balances and to provide awarning signal indicative of the existence thereof.

Detector 1 comprises a detection circuit 3 and a warning circuit 4.

The function of the detection circuit is to detect when the pressurewithin the transformer tank 2 is substantially equal to the pressureoutside the transformer tank and to actuate the warning circuit 4 ifthat pressure condition exists for a predetermined time period. When Isay that the pressure within the tank is substantially equal to thepressure outside the tank I mean that the pressure within the tank iswithin a narrow range between slightly positive pressure and slightlynegative pressure. This condition has been previously referred to as asubstantial pressure balance."

The function of the warning circuit is to provide a leak warning signalupon being actuated.

The detection circuit comprises a source of electrical energy 5 whichincludes a transformer 6 whose primary 7 is coupled to an A-C power line8 and whose secondary 9 is coupled to a full wave diode rectifierbridge, 10. The detection circuit comprises an energy storage device 11,a switch means 12 and a warning circuit actuating relay 13. The switchmeans is connected between the energy source 5 and both the storagedevice 11 and the relay 13. The switch means includes two pairs ofstationary contacts, 14 and 15, and a movable contact 16.

When the movable contact of switch 12 bridges either pair of stationarycontacts, the power source 5 is connected to the energy storage device11 and to the relay 13. This results in the energization of the relay.The relay may also be energized from the energy storage device 11itself, since that device comprises a rechargeable battery (which ispreferably of the nickelcadmium type). The battery is adapted toenergize the relay whenever both pairs of contacts of the switch means12 are open (assuming of course, that the battery is in a chargedcondition).

The relay is arranged such that whenever it becomes deenergized thewarning circuit 4 is actuated to produce a leak warning signal. To thatend, relay 13 includes a pair of stationary contacts 17 and a movablecontact 18. The latter contact serves to close the stationary contactswhenever the relay is deenergized.

The warning circuit 4 includes a warning signal producing means 19connected to an A-C line 20 via stationary contacts 17. The signalproducing means may include either a visual signal producer or anaudible signal producer, or.a combination of both which, upon closure ofcontacts 17, produces a warning signal indicative of the existence of atransformer tank leak.

Movable means 21 are provided in my detector to effectuate the movementof the movable contact 16 'of switch '12. Preferably such movable meanscomprises a bellows connected to movable contact 16. The bellows is alsoconnected to the transformer tank in a manner such that its interiorcommunicates with the interior of the tank. When arranged in this mannerthe bellows expands in the presence of positive tank pressure and in sodoing causes the closure of contacts 14 by contact 16. In the presenceof negative tank pressure the bellows contracts and in so doing causesthe closure of contacts 15 by contact 16. When there is a s'ubstantialpressure balance in the tank the bellows moves contact 16 to a neutralposition whereupon both pairs of contacts 14 and 15 remain open.

Operation of my leak detector will be better understood from thefollowing examples. First it shall be assumed that transformer tank 2does not have a leak in it and that the transformer is supplying a smallload, having just previously supplied a large load. During the periodthat the transformer had supplied a large load positive pressure wouldhave built up in the tank. Such pressure causes the bellows 21 to expandand results in the closure of contacts 14. Closure of contacts 14enables the power source 5 to energize the relay [3 and to charge thebattery 11 (if it had been previously discharged). The energization ofrelay l3 enables the stationary contacts 17 to remain open and thewarning circuit 4 to be deactuated. v

As the dielectric fluid inside the transformer tank cools (a result ofthe decreased load imposed on the transformer) the pressure within thetank decreases toward negative pressure. By the time that the pressurein the tank equals the pressure outside the tank, i.e., atmosphericpressure, the bellows will have contracted sufficiently to move themovable contact 16 to a neutral position and both pairs of stationarycontacts 14 and 15 will be open. When this occurs energy source 5 willcease energizing relay 13. Nevertheless, the relay will remain energizedsince the battery will begin to discharge its energy through the relay.The relay will remain energized for as long as the battery can providesufficient relay energizing current. Therefore the battery utilized inmy detector is selected to provide relay energizing current for a periodof time which is greater than the time period during which atransitional substantial pressure balance would exist.

After the short endurance period of the transitional substantialpressure balance the pressure within the tank will decrease further,whereupon the bellows will contract further and cause the closure ofcontacts 15. At this time the energy source 5 will take over theenergization of the relay 13 and will also begin recharging the battery11.

It should therefore be appreciated from the above example that atransitional substantial pressure balance" does not cause the erroneousproduction of a leak warning signal.

Now it shall be assumed that a leak arises in the tank at a time whenthere is a positive pressure therein. In

such an event the pressure would decrease until it is within the narrowsubstantial pressure balance" range. This results in the bellows movingmovable contact 16 to the neutral position whereupon source 5 will ceaseenergizing relay l3 and battery 11 will begin energizing relay l3. Owingto the existence of the leak, the pressure within the tank will remainin that narrow range for as long as the leak exists, irrespective ofchanges in the magnitude of the load. Accordingly, if the leak is stillin existence at the time that the battery has discharged to the pointwhere the amount of energy remaining in it is insufficient to providerelay energizing current, the relay will be deenergized. Upon thedeenergization of relay l3, movable contact 18 will close stationarycontacts 17, thereby actuating the warning circuit and producing asignal indicative of the existence of the leak.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects; and I, therefore, intend herein tocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A leak detector for determining when the pressure within a closed,fluid containing enclosure is substantially equal to the pressurewithout said enclosure, and for providing a warning signal when such acondition has existed for a preselected period of time, said detectorcomprising:

a. movable means responsive to the pressure within the enclosure;

b. dischargeable energy storage means;

0. first means coupled to said movable means for energizing said energystorage means except when the pressure within the enclosure issubstantially equal to the pressure without the enclosure; and

d. means adapted for providing a warning signal in response to thedischarge of said energy storage means.

2. The leak detector as specified in claim 1 wherein said energy storagemeans includes a storage battery and wherein said signal producing meansis responsive to the discharge of a predetermined portion of the energystored by said battery.

3. The leak detector as specified in claim 2 wherein said movable meansincludes a bellows and wherein said first means comprises a switch meansconnected to said bellows and a source of energy, said source of energybeing connected to said battery via said switch means.

4. A leak detector for determining when the pressure within a sealedtransformer tank containing a dielectric liquid is substantially equalto the pressure without said tank and for providing a warning signalwhen such a condition has existed for a preselected period of time, saiddetector comprising:

a. movable means responsive to the pressure within the tank;

b. dischargeable energy storage means;

c. energy supply means coupled to said energy stora e means; switc meanscoupled to said movable means connecting said energy supply means toenergize said energy storage means except when the pressure within thetank is substantially equal to the pressure without the tank; and

e. means for providing a warning signal in response to the discharge ofa preselected amount of energy stored in said storage means.

5. In an electric translating apparatus coupled to an electric load,said apparatus being housed within a sealed tank containing a dielectricfluid, the magnitude of the pressure within the tank being variable inresponse to changes in the magnitude of said load, a leak detectorcoupled to said tank for determining when the pressurewithin the tank issubstantially equal to the pressure without said tank and for providinga warning signal when such a condition has existed for a preselectedperiod of time, said detector comprising:

a. movable means responsive to the pressure with the tank; b.dischargeable energy storage means; c. energy supply means coupled tosaid energy storage means;

. switch means coupled to said movable means connecting said energysupply means to energize said energy storage means except when thepressure within the tank is substantially equal to the pressure withoutthe tank; and

e. means for providing a warning signal in response to the discharge ofa preselected amount of energy stored in said storage means.

1. A leak deTector for determining when the pressure within a closed,fluid containing enclosure is substantially equal to the pressurewithout said enclosure, and for providing a warning signal when such acondition has existed for a preselected period of time, said detectorcomprising: a. movable means responsive to the pressure within theenclosure; b. dischargeable energy storage means; c. first means coupledto said movable means for energizing said energy storage means exceptwhen the pressure within the enclosure is substantially equal to thepressure without the enclosure; and d. means adapted for providing awarning signal in response to the discharge of said energy storagemeans.
 2. The leak detector as specified in claim 1 wherein said energystorage means includes a storage battery and wherein said signalproducing means is responsive to the discharge of a predeterminedportion of the energy stored by said battery.
 3. The leak detector asspecified in claim 2 wherein said movable means includes a bellows andwherein said first means comprises a switch means connected to saidbellows and a source of energy, said source of energy being connected tosaid battery via said switch means.
 4. A leak detector for determiningwhen the pressure within a sealed transformer tank containing adielectric liquid is substantially equal to the pressure without saidtank and for providing a warning signal when such a condition hasexisted for a preselected period of time, said detector comprising: a.movable means responsive to the pressure within the tank; b.dischargeable energy storage means; c. energy supply means coupled tosaid energy storage means; d. switch means coupled to said movable meansconnecting said energy supply means to energize said energy storagemeans except when the pressure within the tank is substantially equal tothe pressure without the tank; and e. means for providing a warningsignal in response to the discharge of a preselected amount of energystored in said storage means.
 5. In an electric translating apparatuscoupled to an electric load, said apparatus being housed within a sealedtank containing a dielectric fluid, the magnitude of the pressure withinthe tank being variable in response to changes in the magnitude of saidload, a leak detector coupled to said tank for determining when thepressure within the tank is substantially equal to the pressure withoutsaid tank and for providing a warning signal when such a condition hasexisted for a preselected period of time, said detector comprising: a.movable means responsive to the pressure with the tank; b. dischargeableenergy storage means; c. energy supply means coupled to said energystorage means; d. switch means coupled to said movable means connectingsaid energy supply means to energize said energy storage means exceptwhen the pressure within the tank is substantially equal to the pressurewithout the tank; and e. means for providing a warning signal inresponse to the discharge of a preselected amount of energy stored insaid storage means.